Fly Baby Windshields

When it comes to the windshields, Fly Baby builders have two sets
of
two choices.

Windshield Style

The first choice: Should you build the stock three-piece
windshield
or go for a wrap-around type?

While many prefer the look of the wrap-around model, I really
recommend
going with the stock three-pane version. There's no plastic
forming
on the stock model...you just cut out three flat pieces of clear
plastic,
bend some metal for edges and frames, and bolt it all
together. With
the wrap-around model, you have to either find a pre-molded
windshield
that fits, or build a mold and oven to soften the plastic and form
it into
shape. Certainly possible, but it may take a few tries to
get an
acceptable version that will fit on your plane.

The second reason for going with the stock windshield comes when
one
has to *replace* a windshield. With a one-piece, not only do
you
have to set up the forms and oven to bend the plastic, you have to
bend
the plastic to match the bends of the OLD windshield.
Otherwise,
it may not fit the bolt holes that are already in your cowling.

I'm sweating my own windshield right now...it's the wrap-around
type
on the right above, and over twenty-five years, it's gotten
a bit
crazed and scratched. I just don't think I can make a
three-dimensional
mold to match, which would mean I'd probably have to drill new
mounting
holes in the fuselage sheet aluminum. I'd *love* to replace
my windshield,
but don't want to have to patch all the mounting holes for the old
one.

Contrast that with the days when I was operating N500F, with the
flat-angled
configuration. When a windshield panel developed a crack, I
removed
it (it was mounted with 1/8" bolts), laid it atop a fresh sheet of
flat
Lexan, traced out the shape, and marked the bolt holes. Then it
just had
to be cut out, the holes drilled, and re-installed. Took
just an
evening...and I kept the old windshield pane for a pattern so I
could make
new panes in the future without having to disassemble the
windshield.

Windshield Material

Which brings us to the second issue: What material should you
make
your windshield from?

You basically have two choices: Plexiglas and Lexan. Back
in August
2005, Don Glewe posted a good explanation of the two types:

Both are trade names --like Kleenex or Puffs-- for two
different
types of plastic: polycarbonate and acrylic. Both are
available in
many brands.

Plexiglas is ACRYLIC. it is harder and therefore
more brittle,
making it tougher to cut/machine --you can still do it, as long
as you're
careful and use fine-toothed blades and be careful not to feed
it too fast.
Holes can be drilled safely by merely relieving the "corners" on
the ends
of the bits so they don't grab. it is easy to heat form: a
handheld air
heater can be passed over the desired bend location, and a
pretty decent
bend can be formed by draping the sheet over a half-mold or just
clamping
the sheet to the edge of a workbench and letting it fall
onto a board
held to the desired angle. Downsides: it scratches easily
--but can
just as easily be sanded/polished. The biggest con is that
it will
shatter/break into nasty sharp pieces if broken --dunno if I'd
want that
in front of me.

Lexan is POLYCARBONATE. it is "softer" --that
makes it
easier to cut/machine, because it won't chip as much. It
also makes
it good from an impact protection standpoint, because it won't
shatter
as easily as acrylic --I forget exactly, but I think 1/8" of the
stuff
will stop a 22-round. The downside comes from the same
softness:
polishing out/removing scratches in polycarbonate is a
nightmare!
It is also harder to heat form --so if you go with a one-piece
you'll probably
end up having it done by a company with a big enough oven to
heat it consistently.

Telling the two apart --if they don't say what they are on the
label--
can be done by looking at the sheet edge: poly will look dark,
acrylic
light or "clear". You can also whip out a pocketknife and
try to
carve a little sliver off the edge: poly will peal up like a
soft wood/metal,
while acrylic will be very resistant and may only chip/flake.

All right: which type should you use?

Both have advantages and disadvantages. But I vote Lexan.

Why? Well, Lexan has two disadvantages. It scratches
a bit
easier than Plexiglas, and it doesn't tolerate fuel spills as
well.
That's one reason I need a new windshield; I spilled a bit of gas
on the
old one years ago and it got a bit wavy. Only near the
bottom in
one spot, but as time went on, the windshield looks like it's
becoming
crazed around that location.

The advantages of Lexan? One great big one: Unlike
plexiglass,
Lexan doesn't break.

This isn't much of an operational advantage (if you're
encountering
.22 caliber rounds in flight, you've got BIGGER problems than a
windshield),
but it's a big baby blue plus when you cut and drill it.
Forget the
special drill bits, forget the special sawing techniques.
Just run
the Lexan pane through the bandsaw (or even saber saw), and drill
the holes
with a conventional drill.

You'll find a lot of helpful advice for cutting Plexiglas;
comments
about how to modify drill bits to cut it, and how to minimize the
potential
for breaking when you cut it. Plexiglas will develop
networks of
cracks if not worked with the proper tools.

But Lexan? Cut it on a bandsaw, smooth the edge on the
benchtop
belt sander, pop the holes with a hand drill. Beat it, abuse
it,
whang on it. It just doesn't care.

Another plus...Lexan is common. You can buy it at Home
Depot.
In fact, the 2'x 4' sheet they sell is enough for two or even
three windshields.

Yes, Lexan will scratch easier and need replacement more
often.
But Lexan is cheap, and if you go with the three-piece windshield,
you
can easily replace the panes every couple of years if you
want. Just
remove the old pane, trace out the outline on a new piece of
Lexan, cut
it with a bandsaw or saber saw, match-hole-drill the bolt holes,
and mount
the new pane. $100 from Aircraft Spruce or Wicks will buy
you a lifetime
supply of Lexan for windshields.

Cutting the Bolt Holes - A Caution

One warning, especially if you use plexiglass: Cut the bolt
holes
slightly larger than the fastener size, and DON'T completely tighten
the
bolts.

Plastic has a different coefficient of thermal expansion than
metal.
When the plane sits in the sunlight, the plastic will want to grow
larger
(Tony Bingelis says a 24" square sheet will lengthen by about
1/8").
If the holes are exact size, or the bolts are tight, it can't
expand and
stresses are induced. See Bingelis' "The Sportplane
Builder."